Two-electrode gas analysis system for electrically sensing and controlling redox reactions

ABSTRACT

A gas analysis system includes a pair of electrodes disposed in a cell containing an electrolyte through which a sample gas containing an unknown quantity of a reactant gas is passed. The gas reacts with the electrolyte, which changes the electrical resistance of the electrolyte in proportion to the concentration of the reactant gas. The electrodes are part of an externallypowered monitoring circuit which alternately senses the resistance of the electrolyte and then generates a voltage between the electrodes in response to the sensed resistance, permitting a generating current to flow periodically in response to the sensed resistance, the generating current being proportional to the amount of gas reacting with the electrolyte.

United States Patent [1 1 Heuser TWO-ELECTRODE GAS ANALYSIS SYSTEM FORELECTRICALLY SENSING AND CONTROLLING REDOX REACTIONS [76] Inventor:Rudolph L. Heuser, 1300 Fair Way,

Space 23, Calistoga, Calif. 94515 [22] Filed: Sept. 17, 1973 [2]] Appl.No.: 398,006

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[ 1 Oct. 14, 1975 Primary ExaminerT. Tung Attorney, Agent, orFirm-Christie, Parker & Hale 57 ABSTRACT A gas analysis system includesa pair of electrodes disposed in a cell containing an electrolytethrough which a sample gas containing an unknown quantity of a reactantgas is passed. The gas reacts with the electrolyte, which changes theelectrical resistance of the electrolyte in proportion to theconcentration of the reactant gas. The electrodes are part of anexternallypowered monitoring circuit which alternately senses theresistance of the electrolyte and then generates a voltage between theelectrodes in response to the sensed resistance, permitting a generatingcurrent to flow periodically in response to the sensed resistance, thegenerating current being proportional to the amount Of gas reacting withthe electrolyte.

12 Claims, 6 Drawing Figures US. Patent 00:. 14, 1975 Sheet 2 of23,912,613

TWO-ELECTRODE GAS ANALYSIS SYSTEM FOR ELECTRICALLY SENSING ANDCONTROLLING REDOX REACTIONS BACKGROUND OF THE INVENTION This inventionrelates to gas analysis, and more particularly to an improved method andapparatus for determining the amount of a sample gas reacting with anelectrolyte.

In the field of air pollution control it is necessary to measure theamount of pollutant in an exhaust gas stream. For example, it may benecessary to measure the quantity of noxious sulfides or sulfur dioxidein exhaust gases of factories or refineries.

A variety of ways are presently known by which the concentration ofpollutant in a sample gas stream can be analyzed through redox reactionsbetween the sample gas and an electrolyte. Generally speaking, the priorart electrolytic monitoring systems fall within two categories thoseknown as galvanic cells in which the electrical potential between theelectrodes is provided by a self-contained source, and cells in whichthe potential between the electrodes is generated by an external powersource.

Generally speaking, the current flow between the electrodes in either agalvanic or an external power source cell is proportional to the amountof reactant gas flowing in the system. In one commercial apparatus formeasuring reducing reactant gases, an external electrical power supplygenerates free halogen at a predetermined rate, and the resulting signallevel is monitored by a coulometric system. When a reactant gas isadmitted to the apparatus, the decrease in signal level is a measure ofthe reactant concentration. Since galvanic systems are limited in theamount of electrical current they can produce, they are inadequate inanalyzing sample gas streams containing high concentrations of reducingreactant gases.

In contrast, external power systems are not limited in their capacity togenerate sufficient electrical energy to monitor the contents of samplegas streams containing a relatively large concentration of reactant gas.However, such monitoring systems in the past have been relativelycomplex because they have been comprised of three or more electrodes andelaborate hardware which make such systems relatively costly to produceand operate, together with being difficult to operate and being lackingin versatility.

SUMMARY OF THE INVENTION This invention provides an externally-poweredtwoelectrode system for electrically sensing and controlling redoxreactions. The system is relatively simple in structure and inexpensiveto produce and operate. The system also is capable of analyzing gasstreams containing relatively large concentrations of reactant gas inaddition to relatively small concentrations.

Briefly, the system includes a cell containing a body of electrolytethrough which a sample gas stream to be analyzed is passed, and a pairof electrodes in the electrolyte. A monitoring circuit connected to theelectrodes includes a sensing circuit for producing an output responsiveto the electrical conductivity ofthe electrolyte present between theelectrodes. A generating circuit responsive to the output of the sensingcircuit produces either a sufficient generating voltage between theelectrodes to electrolyze the electrolyte when the sensed conductivityof the electrolyte is within a first range, or it produces aninsufficient voltage so the electrolyte will not be electrolyzed whenthe sensed conductivity is within a second range. The output voltageproduced by the generating circuit produces a generating current whichis proportional to the amount of gas reacting within the electrolyte.The output current is monitored to produce a continuous reading of theamount of reactant gas in the sample gas stream.

Preferably, the sensing circuit periodically measures the electricalresistance of the electrolyte/sample gas solution. The generatingcircuit responds to the resistance periodically measured by the sensingcircuit to produce a periodic generating current which maintains apreset level of oxidant in solution by electrolysis of the electrolyte.The current flowing in the generating circuit is directly proportionalto the quantity of gas reacted and is measured in the generating circuitin each period succeeding operation of the sensing circuit.

Thus, the voltages applied across the electrodes alternate between afirst voltage for measuring the amount of reacted gas in the system, anda second voltage pulse immediately following the first pulse for eitherproducing generating current flow between the electrodes or not,depending upon the level of conductivity sensed by the first pulse.

These and other aspects of the invention will be more fully understoodby referring to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectionalelevation view, partly broken away, showing an electrolytic cell used inthe gas analysis system of this invention;

FIG. 2 is a schematic electrical diagram of the pre ferred monitoringcircuit of this invention;

FIG. 3 is a graphic representation of typical electrode potentialsoccurring during operation of the monitoring circuit;

FIG. 4 is a schematic block diagram of an alternate monitoring circuit;

FIG. 5 is a schematic cross-sectional elevation view, partly brokenaway, showing an alternate embodiment of an electrolytic cell used inthe gas analysis system of this invention; and

FIG. 6 is a schematic block diagram of a further alternate monitoringcircuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventionprovides an externallypowered two-electrode system for electricallysensing and controlling redox reactions between a sample gas and anelectrolyte. The system is useful in electrochemically determining theexact quantities of those gaseous constituents of the sample gas whichare oxidized to either a lower negative valence or a higher positivevalence when they are allowed to react with a controlled quantity of anoxidant in an electrolyte. Several fields where this invention may beuseful are in air pollution control both for emission control and airquality preservation, sewer gas control and monitoring, natural gascontrol and odorant monitoring, the protection of expensive platinumcatalysts in petroleum refining, the control of stack emission andeconomizing of black liquor recovery in pulp and paper production, andthe monitoring and control of both odorants and contaminants in the LPGindustry.

One form of the present invention is described in the context of anelectrolytic cell shown schematically in FIG. 1. The cell is made fromglass tubing and includes a small diameter tube 12 which serves as asample gas inlet and which opens into the lower portion of an uprightreaction tube 14. The top of the reaction tube opens into one side of afunnel-shaped gas separation chamber 16 of the cell. A sample gas exittube 20 leads away from the opposite side of the separation chamber. Astopper shown in phantom line at 18 closes the top of the separationchamber. The bottom of the separation chamber tapers narrower downwardlyand opens into an elongated upright medium-diameter tubular monitoringchamber 22 having an interior area wide enough to accommodate a pair ofelectrodes to be described in detail below. The electrodes are supportedby a rod 19 made of non-conductive material. The medium-diameter sectiontapers narrower at its bottom and opens into a tubular section 23 ofreduced diameter which is connected by a plastic tube 25 to the base ofreaction tube 14 to provide a suitable means for allowing theelectrolyte to return to the reaction tube. A small diameter tube 24provides a connection to a reservoir (not shown) containing additionalelectrolyte so the liquid level in the cell is maintained within normaloperating tolerances, and so the electrolyte is replenished as it isconsumed.

The cell is filled with an electrolyte 21 comprised of an acqueoussolution of a halide and free halogen, and in the following descriptionthe electrolyte will be considered to be aqueous hydrobromic acidcontaining a relatively high concentration of free bromine. A pair ofelectrodes are disposed in the electrolyte contained in tubular section22. The electrodes preferably are both made of platinum, although othermaterials, including dissimilar elemental materials, may be used. In theuse of dissimilar electrodes, for example, platinum and carbon may beeffectively used. Preferably, both electrodes shown in FIG. 1 are madefrom platinum mesh screen rolled into two cylinders. The electrodesinclude a relatively large-diameter cylindrical screen 26 acting as theouter electrode. (A helix of platinum wire also has been usedsuccessfully as the outer electrode). Screen 26 is connected to aconductor lead 27 of negative polarity so that screen 26 acts as thecathode of the monitoring circuit of this invention. A small-diametercylindrical screen 28 is wound as tightly as possible around rod 19 andis disposed within the interior of screen 26. The small-diameter screen28 is connected to a conductor lead 29 of positive polarity so thescreen 28 provides the anode of the monitoring circuit of thisinvention. (The preferred polarity for this particular two-electrodecell configuration has not been proven.) The two electrodes are disposedone inside the other and in close proximity to each other. They areinsulated from each other with plastic spacers (not shown) which do notappreciably impede the flow of electrolyte through the cell. Theelectrodes preferably are positioned below the junction of separationchamber 16 and monitoring chamber 22, and are located well below thesurface of the electrolyte so the concentration of electrolytecontacting the electrodes during operation of the cell is a relativelyhomogeneous mixture.

During use of the cell the gas stream being monitored is forced throughthe sample gas inlet tube 12. The

sample gas flow preferably is metered at a rate of about cc per minute.The gas pressure at the sample gas inlet opening either may be slightlyabove atmospheric pressure, or the sample gas may be forced to flowthrough the cell by means of a reduced pressure applied to gas exit tube20. As the sample gas leaves inlet tube 12 and enters the adjacentreaction tube 14, it mixes with the electrolyte in tube 14. For thepurpose of the following explanation it will be assumed that the samplegas stream contains an amount of sulfur dioxide (reactant gas), theconcentration of which is to be analyzed. As the sample gas enters thebottom of tube 14 the gas mixes with the electrolyte so that the sulfurdioxide reacts with free bromine at the liquid-gas interfaces and formsa train of bubbles 30 which rise and transport the reacted electrolyteup in tube 14 and into the top portion of separation chamber 16. In theseparation chamber the residual gas(es) and electrolyte separate, withthe non-reacted portion of the sample gas flowing out exit tube 20. Theelectrolyte washes over the electrodes as it continuously circulatesthrough the cell. The residual gas passing out through exit tube 20 willbe devoid of any sulfur dioxide which has reacted with the free brominein the electrolyte. Any sulfur dioxide present in the sample gas andwhich has reacted with the bromine reduces the bromine concentration ofthe electrolyte in monitoring chamber 22. Any change in the bromineconcentration of the electrolyte present between the two electrodes willchange the electrical resistance of the electrolyte between theelectrodes in proportion to the change in the bromine concentration.Thus, an electrical generating current will start to flow between theelectrodes in proportion to the change in bromine concentration toproduce more elemental bromine by electrolysis. The bromine producedimmediately goes into solution to replace the amount of bromine reactingwith the sulfur dioxide. The current will be in direct proportion to theflow rate of the sulfur dioxide in the sample gas, and can be measuredwith a recorder or other suitable read-out device, such as a meter 32shown in FIG. 2.

FIG. 2 shows a preferred monitoring circuit 34 which is connected to theelectrodes and is used to provide an output representing theconcentration of reactant gas (sulfur dioxide, or other reducing gas)present in the sample gas. The monitoring circuit includes a transformerhaving an input winding 36 which receives power from an external 1 10volt AC. power supply. An output winding 38 of the transformer producesan output voltage of 12 volts A.C. A center tap 40 coupled to the outputwinding of the transformer applies the 12- volt A.C. signal evenlybetween a sensing circuit 42 and a generating circuit 44. A 6-voltpotential from the transformer is applied to the sensing circuit througha diode CR across a voltage divider which includes a resistor R, on oneside of the divider and a resistor R in series with a variable resistorR on the other side of the divider. A current-limiting resistor R isconnected across the divider in series with the emitter of a P-N-Ptransistor Q, to be used to control operation of the generating circuit,as will be described in detail below. A biasing resistor R is connectedin series with the base of transistor Q and also with the adjustablepickoff of a potentiometer R connected in series between two diodes CRand CR Blocking diode CR is also connected to anode 26, and diode CRpotentiometer R diode CR and the electrolyte comprise a second dividercircuit in parallel with the first. The collector of transistor Q, isconnected in series with the base of an N-P-N transistor Q the collectorof which is connected in series with a current-limiting resistor R Avariable resistor R connected in series with the emitter of transistor Qis connected to a common ground along with cathode 28 and the center tap40 of the transformer.

Generating circuit 44 includes a resistor R connected between the centertap of the transformer and a diode CR A coupling capacitor C isconnected between the emitter of transistor Q of the sensing circuit andthe base of N-P-N transistor Q of the generating circuit. A variableresistor R is connected to the common ground and the base of Q(Resistors R and R also are connected across capacitor C,.) A variablebiasing resistor R and a blocking diode CR are connected between thebase and the collector of transistor Q and a current-limiting resistor Ris connected between resistor R and the collector of transistor Q Theemitter of transistor Q is connected to the base of an N-P-N transistorQ having a current-limiting resistor R connected to its collector. Theemitter of transistor Q is connected in series with an electricalmetering device 32, and a blocking diode CR which is connected to anode26.

In use, the monitoring circuit is initially adjusted in the followingmanner (the electrolyte present in the cell containing a predeterminedconcentration level of free halogen suitable for the complete use of theparticular component reactant gas to be measured, and a sample gasstream containing no reactant gas flowing at an acceptable flow rate).An oscilloscope 43 is connected across the electrodes, the oscilloscopebeing previously adjusted so that when an A.C. potential of the samefrequency as the A.C. energy source, and having a peak-to-peak voltageof 2.0 volts, is connected to its signal input leads, two complete sinewaves of a measurable magnitude are displayed on the face of theoscilloscope, and so that intervals of 2.0, 1.5, 1.0, and 0.5 volts maybe readily ascertained and marked on the oscilloscope face with asuitable marker. With the oscilloscope so adjusted, the signal leads aretransferred to the cell and connected to the electrodes as shown in FIG.2. Resistor R is preset at its minimum value, and resistors R R and Rare set at their maximum values. A DC. milliammeter (not shown) isplaced be tween the emitter of transistor Q and ground. Potentiometer Ris now gradually adjusted from the minimum current set point until asharp increase in current is noted on the milliammeter. At this pointthe adjustment is carefully continued until the current increaseindicated slows perceptably. This is the optimum pickoff potential forpotentiometer R and the milliammeter may now be removed. The optimumresistance for potentiometer R not only varies for each cell andelectrode configuration, but also for each halogen concentration, andmust be predetermined experimentally for each type of system. Theselection of the proper resistance for potentiometer R determines thevoltage range of the sensing pulse for that particular system, and theresulting sensing pulse potential must be less than the electrolyzingpotential of the electrolyte as indicated by oscilloscope 43. Thesensing voltage between the two electrodes can vary, although therelatively low voltages (in the range of between 0.4 to 0.9 volt whenhydrobromic acid is the halide) are preferred not only because thisvoltage level is below the level at which electrolysis of theelectrolyte solution will occur, but also because in the lower voltagerange the electrical conductivity of the electrolyte is entirelydependent upon the halogen concentration and not on the appliedpotential. The circuit adjustment may now be completed by graduallydecreasing the resistance value of resistor R and observing theoscilloscope. When the half-cycle sine wave associated with thegenerating circuit reaches the electrolyzing potential of theelectrolyte, there will also be a sharp increase in generating currentas noted by meter 32. Resistor R is now readjusted so the generatingpulse potential is just less than the electrolyzing potential. (In thosecases where meter 32 still indicates current flow, this indicated valuemust be subtracted from the current indicated when a reactant gas isflowing to obtain a value which is truly proportional to the reactantflow rate. This is valid because the total halogen content of theelectrolyte is neither increased nor decreased whenever the appliedpotential is less than the electrolyzing potential.) Resistors R R and Rnormally remain at their preset values, although they may be adjusted insome cases to refine the pickoff point of potentiometer R When thiscondition has been obtained the circuit adjustments are completed andthe oscilloscope may be removed.

The potentials at the emitter and base of transistor Q are now inbalance, with transistor 0, being in a conducting state, and its outputamplified by transistor Q which in turn charges capacitor C Therelatively low potential being applied across the electrodes is used tosense the bromine concentration of the electrolyte to determine whetheror not additional bromine should be generated to replace any brominewhich has reacted with the reactant gas in the sample gas stream. Forexample, if the sample gas stream contains a reactant gas, then thebromine level of the electrolyte will be reduced, which will increasethe resistance present between electrodes 26 and 28, and thereby cause agenerating current to flow between the electrodes. The magnitude of thecurrent will be in direct proportion to the reactant gas flow rate, andcan be measured by meter 32. On the other hand, if there is no reactantgas in the sample gas stream, then the bromine concentration ofelectrolyte solution will remain at a high level, and the low electricalresistance between the electrodes will result in the electrical voltagein the generating circuit being below 0.9 volt, which is below theelectrolysis potential of the electrolyte, and will thereby prevent thegenerating circuit from producing more bromine.

The typical functioning of the monitoring system is illustratedgraphically in FIG. 3 which shows an alternating sensing pulse 46produced by the sensing circuit in which the low, i.e., 0.6 volt,potential occurring between the electrodes senses whether or not theconcentration of the oxidant in the electrolyte is sufficient to producea generating pulse 48. If the concentration of the bromine is low (theelectrolyte resistance higher than it was when the set point wasestablished), then a generating pulse is produced during the generatingportion of the operating cycle of the monitoring circuit. However, ifthe sensing pulse indicates that the concentration of bromine in theelectrolyte is relatively high, (the resistance being equal to or lessthan when the set point was established) then any pulse produced will beat a lower potential than the electrolyzing potential.

Specifically with reference to the operation of the monitoring circuitshown in FIG. 2, assuming that the sample gas contains a reactant gas,the bromine concentration in the electrolyte solution drops, whichresults in an increased resistance between electrodes, the potential atthe base of transistor Q increases with respect to the potential at theemitter, causing transistor O to turn off. The charge normallymaintained on coupling capacitor C by the variable resistances R and Rleaks ofi the capacitor when transistor 0, stops conducting and lowersthe potential at the base of transistor Q When the voltage at the baseof transistor 0;; is thus lowered relative to the potential at itsemitter, transistor Q begins conducting. The output of transistor O isamplified by transistor Q, to produce a relatively high voltage (over 1volt when hydrobromic acid is the halide) across electrodes 26 and 28which generates a current sufficient to maintain a preset level ofbromine in solution by means of electrolysis of the electrolyte so thatthe amount of bromine in the electrolyte being used up the be reactantgas is replaced. Thus, as described above, the amount of currentrequired to replace the bromine being reacted is proportional to theflow rate of the reactant gas in the sample gas stream, so the readingprovided on meter 32 of the generating pulses over a period of time willprovide an indication of the concentration of reactant gas in the samplegas stream.

Conversely, if there is a relatively high bromine concentration of theelectrolyte sensed during the sensing pulse of the monitoring circuitcycle, i.e. the sample gas ceases to contain a reactant gas, then theresistance between the electrodes decreases. This lowers the potentialat the base of transistor O to a point lower than the potential acrossthe the emitter of the transistor. Thus, transistor Q, begins conductingto charge capacitor C The charge on the capacitor then raises thepotential at the base of transistor 0;, which will turn off transistor Qand thereby prevent the generating circuit from producing a voltagebetween the electrodes sufficient to electrolyze the electrolyte. Thus,because the bromine concentration is relatively high, no further brominegeneration is necessary.

Thus, the present invention provides an externallypowered two-electrodemonitoring system which is relatively simple in construction andoperation. Moreover, the system has sufficient capacity to monitor gasstreams having high reactant concentrations because the capacity of thegenerating circuit is not limited as in the case of coulometric gasanalysis systems.

Although the gas analysis system has been described in the context ofanalyzing sample gases containing reducing contaminant gases, oxidizingcontaminant gases such as ozone can be measured without departing fromthe scope of this invention. For example, this may be accomplished byintroducing aregulated quantity of reducing reactant gas, i.e., sulfurdioxide, into the cell to create an artificial background signal whichthen decreases in proportion to the amount of oxidant contaminant in thesample gas.

FIG. 4 shows an alternate monitoring circuit 50 in which the voltagepotential for the sensing portion is provided by an EMF potentialobtained by using electrodes 52 and 54 of dissimilar elementalmaterials, such as platinum'and carbon, in an electrolyte solutioncontained in an electrolytic cell 56. Electrodes 52 and 54 are connectedto the terminals of an electronic sensing circuit 57 (similar to sensingcircuit 42 above) which controls an external power supply 58 to providegenerating current to replenish the oxidant as it is consumed by thereactant gas. Sample gas containing a reactant gas is fed through theelectrolyte solution in cell 56, and after the reactant gas reacts withthe oxidant in the electrolyte, the remaining portion of the sample gasexits the cell. The amount of current flowing between the electrodesduring the sensing period will be a function of the concentration of theoxidant in the electrolyte, and this current then will be used totrigger the power source 58 which either will or will not produce agenerating current depending upon the amount of the current generated bythe sensing circuit. Read-out meter 59 provides an indication of theamount of reactant gas contained in the sample gas stream.

FIG. 5 shows an alternate form of the cell provided by this invention inwhich a single upright reaction tube 60 contains a limited quantity ofelectrolyte 62 fed into the bottom of the cell through an inlet tube 64from a reservoir (not shown). The'minimal volume of active electrolytein this type of cell accentuates its sensitivity to slight changes inreactant concentration, especially when the reactant concentration is inthe low PPM concentration ranges. A cathode 66 submerged in theelectrolyte comprises platinum foil shaped as an openended cylinder. Aplatinum lead wire 68 connected to the cathode cylinder 66 is adaptedfor suitable connection to a monitoring circuit in accordance with thisinvention. A glass frit 61 connected to the bottom of inlet tube 70provides a sample gas inlet to the cell. Tube 70 extends downwardlythrough a major portion of the interior of the cell to a pointimmediately above the open top of the cathode cylinder. The frittedportion 61 of inlet tube 70 extends through the cylinder and mounts ananode made of platinum wire mesh screen 72 located concentrically insidecylindrical cathode 66. Alternatively, the anode may be provided by avapordeposited platinum coating on the surface of glass frit 61. Aplatinum lead wire 74 is connected to anode 72 and adapted for suitableconnection to the monitoring circuit.

During use of the cell shown in FIG. 5, the open ends of the foilcathode not only provide a pathway for the unreacted sample gas to exitthe immediate area of the electrodes upwardly, but they also cause theelectrolyte between the electrodes to continually flow upwardly betweenthe electrodes and downwardly outside the cathode. This action preventselectrode polarization, and promotes a fast and sensitive response ofthe electrical circuits to slight changes in bromine concentration,whenever the sample gas contains a reactant gas component. Moreover, thelocation of the cathode and the anode in the immediate area where thereaction between the reactant gas and the oxidant takes place providesan extremely accurate way of measuring the in stantaneous concentrationof oxidant in solution, and thereby provides a highly accuratemeasurement of the reactant gas in the sample gas stream. Any portion ofthe sample gas stream which is not reacted passes out of the cellthrough a gas exit tube 76.

FIG. 6 shows a further alternate form of the invention in which acontainer of elemental material, such as platinum or carbon, acts as thecathode for the monitoring circuit. A sample gas inlet tube 82 ofsimilar or dissimilar elemental material acts as the anode. Anelectrolyte 84 containing dissolved free halogen and halide in aqueoussolution is disposed in the container with the bottom of the sample gasinlet tube 82 being submerged in the electrolyte. A sample gascontaining reactant passes through the sample gas inlet tube and formsbubbles 86 to provide electrolyte circulation. A sensing and generatingcircuit 88 similar in configuration to the circuit shown in FIG. 2 isconnected by suitable conductor leads to container 80 and inlet tube 82.The sensing and generating circuit is powered by an external powersupply 90, and a read-out device 92 provides an indication of the amountof reactant gas contained in the sample gas stream.

I claim:

1. An externally-powered, two-electrode system for measuring the amountof a gaseous component reactable with an electrolyte, the systemincluding a cell containing the electrolyte through which a gas streamcontaining said component to be measured is passed, a cathode and ananode disposed in spaced apart relation within the electrolyte in thecell, and an externallypowered electrical monitoring circuit connectedto the cathode and the anode and in which sensing and generatingfunctions of the circuit are alternately shared only by said cathode andanode, the monitoring circuit including a sensing circuit adapted toapply a first voltage pulse between the cathode and anode to produce anoutput related to the conductivity of the electrolyte, a generatingcircuit response to the output produced by the sensing circuit forproducing, immediately following said first voltage pulse, a secondvoltage pulse between the cathode and the anode either sufficient toelectrolyze the electrolyte when the sensed conductivity of theelectrolyte is within a first range, or insufficient so the electrolyteis not electrolyzed whenthe sensed conductivity of the electrolyte iswithin a second range, and means for recording the generating circuitcurrent as an indication of the amount of said gaseous component.

2. Apparatus according to claim 1 in which the electrolyte has acharacteristic voltage level above which it can be electrolyzed andbelow which it cannot be electrolyzed, and in which the generatingcircuit voltage pulse is above said level if the electrical resistancesensed by the sensing circuit is above a certain level, and in which thegenerating circuit voltage pulse is below said level if the electricalresistance sensed by the sensing circuit is below a certain level.

3. Apparatus according to claim 2 in which the sensing circuitperiodically measures the electrical resistance between the cathode andanode, and in which the generating circuit responds periodically to theresistance measured by the sensing circuit to produce a periodic outputwhich is a function of the resistance periodically measured by thesensing circuit.

4. Apparatus according to claim 3 in which the sensing circuit includesmeans for maintaining the voltage of the first pulse below saidcharacteristic voltage level between the cathode and the anode, and inwhich the sensing circuit includes means producing a first output signalwhen the electrical resistance of the electrolyte present between thecathode and the anode is above a certain level, and a second outputsignal when the electrical resistance of the electrolyte present betweenthe cathode and the anode is below a certain level, and in which thegenerating circuit is responsive to either the first output signal forapplying a voltage pulse between the cathode and the anode sufficient toelectrolyze the electrolyte, or to the second output signal for applyinga voltage pulse between the cathode and the anode insufficient toelectrolyze the electrolyte.

5. Apparatus according to claim 1 in which the cell includes a reactionchamber containing the electrolyte, with the cathode and anode beingsubmerged in the electrolyte in the reaction chamber, and in which thecell further includes a gas inlet tube extending to the vicinity of thecathode and anode so that a sample gas stream passing through the inlettube will react with the electrolyte in the presence of the cathode andanode.

6. Apparatus according to claim 5 in which either of the cathode oranode is a cylindrical open-ended body, and the other is located in theinterior of the cylinder.

7. Apparatus according to claim 6 in which the gas is admitted at alocation to provide circulation of the electrolyte through the cylinder.

8. Apparatus according to claim 5 in which the cell includes an inletconduit opening into a portion of the cell containing the electrolytefor admitting electrolyte to the cell as the electrolyte is beingconsumed.

9. Apparatus according to claim 8 in which the inlet conduit is ofsmaller diameter than the diameter of the cell which contains theportions of the electrodes submerged in the electrolyte, and in whichthe inlet conduit opens into the cell immediately below where theelectrodes are submerged in the electrolyte.

10. Apparatus according to claim 1 in which the cell includes acontainer for holding a body of the electrolyte and a sample gas inlettube in communication with circulating electrolyte in the container, andin which the container and sample gas inlet tube are connected inelectrical circuit relation with the monitoring circuit so the containerand inlet tube act as the cathode and the anode.

11. Apparatus according to claim 1 in which the cell includes an inletconduit opening into a portion of the cell containing the electrolytefor admitting electrolyte to the cell as the electrolyte is beingconsumed.

12. Apparatus according to claim 11 in which the inlet conduit is ofsmaller diameter than the diameter of the cell which contains theportions of the electrodes submerged in the electrolyte, and in whichthe inlet conduit opens into the cell, immediately below where theelectrodes are submerged in the electrolyte.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT N0. 1 13 0 DATED October 14, 1975 lNV ENTOR(S) Rudolph L. HeuserIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Col. 2, line 22, "first voltage for" should read first 'voltage pulsefor 0 Col. 7, line 21, "up the be reactant" should read up by thereactant Signed and Sealed this 0 Third Day of August 1976 [SEAL]Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parentsahd Trademqrkx

1. AN EXTERNALLY-POWED, TWO-ELECTRODE SYSTEM FOR MEASURING THE AMOUNT OFA GASEOUS COMPONENT REACTABLE WITH AN ELECTROLYTE, THE SYSTEM INCLUDINGA CELL CONTAINING THE ELECTROLYTE THROUGH WHICH A GAS STREAM CONTAININGSAID COMPONENT TO BE MEASURED IS PASSED, A CATHODE AND AN ANODE DISPOSEDIN SPACED APART RELATION WITHIN THE ELECTROLYTE IN THE CELL, AND ANEXTERNALLY-POWERED ELECTRICAL MONITORING CIRCUIT CONNECTED TO THECATHODE AND THE ANODE AND IN WHICH SENSING AND GENERATING FUNCTIONS OFTHE CIRCUIT ARE ALTERNATELY SHARED ONLY BY SAID CATHODE AND ANODE, THEMONITORING CIRCUIT INCLUDING A SENSING CIRCUIT ADAPTED TO APPLY A FIRSTVOLTAGE PULSE BETWEEN THE CATHODE AND ANODE TO PRODUCE AN OUTPUT RELATEDTO THE CONDUCTIVITY OF THE ELECTROLYTE, A GENERATING CIRCUIT RESPONSE TOTHE OUTPUT PRODUCED BY THE SENSING CIRCUIT FOR PRODUCING, IMMEDIATELYFOLLOWING SAID FIRST VOLTAGE PULSE, A SECOND VOLTAGE PULSE BETWEEN THECATHODE AND THE ANODE EITHER SUFFICIENT TO ELECTROLYZE THE ELECTROLYTEWHEN THE SENSED CONDUCTIVITY OF THE ELECTROLYTE IS WITHIN A FIRST RANGE,OR INSUFFICIENT SO THE ELECTROLYTE IS NOT ELECTROLYZED WHEN THE SENSEDCONDUCTIVITY OF THE ELECTROLYTE IS WITHIN A SECOND RANGE, AND MEANS FORRECORDING THE GENERATING CIRCUIT CURRENT AS AN INDICATION OF THE AMOUNTOF SAID GASEOUS COMPONENT.
 2. Apparatus according to claim 1 in whichthe electrolyte has a characteristic voltage level above which it can beelectrolyzed and below which it cannot be electrolyzed, and in which thegenerating circuit voltage pulse is above said level if the electricalresistance sensed by the sensing circuit is above a certain level, andin which the generating circuit voltage pulse is below said level if theelectrical resistance sensed by the sensing circuit is below a certainlevel.
 3. Apparatus according to claim 2 in which the sensing circuitperiodically measures the electrical resistance between the cathode andanode, and in which the generating circuit responds periodically to theresistance measured by the sensing circuit to produce a periodic outputwhich is a function of the resistance periodically measured by thesensing circuit.
 4. Apparatus according to claim 3 in which the sensingcircuit includes means for maintaining the voltage of the first pulsebelow said characteristic voltage level between the cathode and theanode, and in which the sensing circuit includes means producing a firstoutput signal when the electrical resistance of the electrolyte presentbetween the cathode and the anode is above a certain level, and a secondoutput signal when the electrical resistance of the electrolyte presentbetween the cathode and the anode is below a certain level, and in whichthe generating circuit is responsive to either the first output signalfor applying a voltage pulse between the cathode and the anodesufficient to electrolyze the electrolyte, or to the second outputsignal for applying a voltage pulse between the cathode and the anodeinsufficient to electrolyze the electrolyte.
 5. Apparatus according toclaim 1 in which the cell includes a reaction chamber containing theelectrolyte, with the cathode and anode being submerged in theelectrolyte in the reaction chamber, and in which the cell furtherincludes a gas inlet tube extending to the vicinity of the cathode andanode so that a sample gas stream passing through the inlet tube willreact with the electrolyte in the presence of the cathode and anode. 6.Apparatus according to claim 5 in which either of the cathode or anodeis a cylindrical open-ended body, and the other is located in theinterior of the cylinder.
 7. Apparatus according to claim 6 in which thegas is admitted at a location to provide circulation of the electrolytethrough the cylinder.
 8. Apparatus according to claim 5 in which thecell includes an inlet conduit opening into a portion of the cellcontaining the electrolyte for admitting electrolyte to the cell as theelectrolyte is being consumed.
 9. Apparatus according to claim 8 inwhich the inlet conduit is of smaller diameter than the diameter of thecell which contains the portions of the electrodes submerged in theelectrolyte, and in which the inlet conduit opens into the cellimmediately below where the electrodes are submerged in the electrolyte.10. Apparatus according to claim 1 in which the cell includes acontainer for holding a body of the electrolyte and a sample gas inlettube in communication with circulating electrolyte in the container, andin which the container and sample gas inlet tube are connected inelectrical circuit relation with the monitoring circuit so the containerand inlet tube act as the cathode and the anode.
 11. Apparatus accordingto claim 1 in which the cell includes an inlet conduit opening into aportion of the cell containing the electrolyte for admitting electrolyteto the cell as the electrolyte is being consumed.
 12. Apparatusaccording to claim 11 in which the inlet conduit is of smaller diameterthan the diameter of the cell which contains the portions of theelectrodes submerged in the electrolyte, and in which the inlet conduitopens into the cell immediately below where the electrodes are submergedin the electrolyte.